Manufacture of sand molds for casting easily oxidizable metal



Patented Nov. 14, 1933 MANUFACTURE 0F SAND MOLDS FOB CASTING EASILY OXIDIZABLE METAL Maurice Noel Lacell, London, England, assignor to British Maxium, Limited, London, England v No Drawing. Application March 15, 1928, Serial No. 262,063, and in France March 18, 1927 16 Claims.

The casting of parts made of easily oxidizable metals, such as, in particular, magnesium and alloys having a base of magnesium, is rendered very dimcult on account of the presence of a certain amount of water in the pores and interstices, of the molds in spite of all precautions taken to dry them thoroughly.

It has been sought to protect the metal against the reactions resulting from the presence of this water by mixing with the foundry sand, numerous bodies added either in the powdered state, or in the liquid state, and in particular bodies more easily oxidizable than the metal, but up to the present time these bodies have only given imperfect results.

As the result of numerous experiments the inventor has observed that a series of bodies giving particularly interesting results are the salts ofammonium. It has been possible, by simply mixing sand, even green sand, with certain salts of ammonium, to secure without other precautions perfectly sound cast pieces.

Use may be made either of salts giving rise, in the presence of the hot metal, to the production of bodies capable of acting upon the metal, or salts giving rise to the production of bodies which are neutral with respect to the latter.

The ammonium salts all can be decomposed by heating to temperatures approaching the temperatures at which it is usual to cast magnesium or its alloys (1. e. at about the melting point of the magnesium or its alloys). Magnesium, as is well known, melts at about 651 C., and it is usual in casting metals to supply the molten metal at a temperature somewhat above its melting point. At the temperature to which the sand of the part of the mold adjacent to the metal becomes heated, ammonium salts decompose, evolving gases or vapors which inhibit oxidation of the metal being cast, and particularly in the case of a fluorine compound, such as ammonium fluoride (which is a halide), a thin adherent layer (perhaps consisting of magnesium fluoride) is formed on the metal casting.

The exact temperatures at which the different ammonium salts so decompose is of no particu lar moment, but with the salts herein enumerated, it is much above the boiling point of water, but below the melting point of magnesium.

A salt of the first class which has given very satisfactory results is ammonium fluoride. It is observed that the cast piece is coated with a thin very adherent and solid film which acts as a protective layer, but of good appearance. The use of ammonium fluoride thus presents the secondary advantage of securing at the same time, on account of thisprotecting layer, the protection of the casting against subsequent oxida- It is well known that ordinary ammonia fluoride (so called) contains a substantial amount of the acid fluoride NH4F-HF and in most cases commercial or technical ammonium fluoride consists essentially of said acid fluoride. Further it is well known that when the normal fluoride is dissolved in water it is to a greater or less extent converted into the acid fluoride, and further it is well known that when ammonium fluoride in solution is brought into contact with sand, ammonium silicofluoride is formed.

A salt of the second class which seems to be particularly suitable is ammonium borate which permits castings of relatively large dimensions to be obtained.

By way of example, and without the following indications being in the nature of a limitation, for moderately silicious sands the proportions of fluoride and borate of ammonium adopted may be less than 2%.

The said salts may be employed in the state of an aqueous solution.

The usual agglomerants or substances protecting the grains of sand, such as solutions of resins in oils, or substances more easily oxidizable than the magnesium can also be added to the sand.

On the other hand, the invention also covers the use of the same substances as surfacing media applied either in the powdered state or in the state of a liquid coating upon the inner surface of the mold, cores etc.

It is to be noted that in practice the present invention presents the advantage of making it possible to increase without disadvantage the proportion of clayey sand contained in the molding sand and consequently to increase its plasticity while reducing its cost.

I claim:

1. A sand mold suitable for casting magnesi and like metals, containing sand intimately mix with ammonium fluorite, at least for the par of the mold adjacent to the cast metal.

2. The herein described improvement which comprises casting metal of the group composed of magnesium and alloys rich in magnesium, in a sand mold, the sand of which, at least for the parts adjacent to the metal beingcast, is intimately mixed with an ammonium salt.

3. The herein described improvement which comprises casting metal of the group composed of magnesium and alloys of magnesium, in a sand mold, the sand of which, at least for the parts adjacent to the metal being cast, is intimately mixed with ammonium fluoride.

4.'The herein described improvement which comprises casting metal of the group composed of magnesium and alloys of magnesium, in a sand mold, the sand of which, at least for the parts adjacent to the metal being .cast, is intimately mixed with ammonium borate.

5. The herein described improvement which comprises casting metal of the group composed of magnesium and alloys rich in magnesium, in a sand mold, the sand of which, at least for the parts adjacent to the metal being cast, is intimately mixed with an ammonium salt selected from the herein described group consisting of fluoride and borate.

6. A method 01 treating a sand mold part to eliminate excessive burning 01' a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part an ammonium salt of an inorganic acid.

7. A method of treating a sand mold part to eliminate excessive burning of a readily oxidiz able metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part an ammonium salt of a non-oxidizing inorganic acid.

8. A method of treating a sand mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part an ammonium salt of an inorganic acid, which salt is an inhibitor of oxidation and which salt contains a halogen element.

9. A method of treating a sand mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium or its alloys when cast in contact'therewith, which comprises incorporating in such mold part an ammonium compound having a decomposition temperature above the boiling point of water.

10. A method of treating a sand mold-part to eliminate excessive burning of a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part a solution'oi an ammonium compound having a decomposition temperature above the boiling point of water.

11. A method 01' treating the surface of a sand mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises applying to the surface of such mold part an aqueous solution of an ammonium salt of an inorganic hydracid.

12. A method of treating a sand mold part'to eliminate excessive burning of a readily oxidiz- A able metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part, a non-oxidizing ammonium salt of a hydracid.

13. A method of treating asand mold part to eliminate excessive burning or a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises incorporating in such mold part an aqueous solution 01. an ammonium salt of a haloid acid.

14. A method of treating the surface of a sand mold part to eliminate excessive burning of a readily oxidizable metal such as magnesium or its alloys when cast in contact therewith, which comprises applying at least to the surface of such mold part with which the metal comes into contact when casting, an aqueous solution of a nonoxidizing ammonium compound having a decomposition temperature above the boiling point of water.

15. The method of preventing excessive burning of magnesium and its alloys, in casting the same in sand molds, which comprises the step of casting same in a sand mold of which at least the parts with which the said. readily oxidizable metal comes into contact, carry an ammonium salt which contains fluorine.

16. In the method of treating a material for forming a mold to eliminate excessive burning 01' a readily' oxidizable metal such as magnesium or its alloys when cast in contact with a mold part formed therefrom, the step which comprises incorporatingin such molding composition a-fluoride of ammonia.

MAURICE NOEL LACELL.

CERTIFICATE OF CORRECTION.

Patent No. 1,935, 591.

November 14, 1933.

MAURICE NOEL LAGELL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 100, claim 1, for "fluorite" read fluoridej and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of January, A. D. 1934.

(Seal) F. M. Hopkins.

Acting Commissioner of Patents. 

